This study wants to investigate the influence of these two anesthesiologic managements on the cerebral oxygen saturation during the "rapid pacing"-period during valvuloplasty. The patients are randomised allocated to one of these two anaesthesiological managements. The investigators use the Near-Infrared Spectroscopy (NIRS) to measure the cerebral oxygen saturation. Parallel there will be a measurement of cerebral biomarkers to monitor cerebral hypoxia.